The crystalline form of Carbon designated as Diamond comprises as its basic unit cell five atoms disposed as a Platonic solid, the tetrahedron. Four of the Carbon atoms are located at each of the four apices of this solid. The fifth Carbon atom is located within the tetrahedron at the “cage” position.
All the bonds in Diamond are sp3 hybridized. They are short, strong, uniform bonds. The unique properties of Diamond derive from the structure and bonding of this species.
Diamond is a valuable material due its properties of hardness (10 on the Mohs hardness scale), heat stability, high room temperature thermal conductivity (about 2000 W/mK), very low rms vibration at room temperature (0.002 nm), a high index of refraction (2.4), and optical transparency from infrared through ultraviolet. Because of its high band gap (5.45 ev) it is a superb electrical insulator (1016 ohm). Boron doped (blue) Diamond has been found to be p-type semiconductor having a high hole mobility and electrical breakdown strength.
Many synthetic methods for Diamond are known. Typically, these methods involve high pressure, high temperatures, or high energy discharges. Moreover, post treatments are frequently necessary for purification. Most of these methods are unsuitable for producing Diamond of a character suitable for microelectronics materials and their applications. To this end vapor deposition and some flame techniques have been used.
One of the earliest examples of a vapor deposition process is that of Gardner, U.S. Pat. No. 3,630,768, in which hydrocarbon gas, possibly containing a dopant, is heated (800°-1450° C.) in the presence of Diamond seed crystals with rigorous exclusion of Oxygen contaminants at sub-atmospheric pressures. An Oxygen gas post-treatment is disclosed for the removal of any Graphite that may be formed.
Kamo et al., U.S. Pat. No. 4,434,188, employ a mixture of Hydrogen carrier gas and hydrocarbons in the presence of a microwave discharge at 300°-1300° C. to deposit Diamond on a substrate at low pressures.
Beetz et al., U.S. Pat. No. 5,051,785, disclose the formation of n-type Diamond by a chemical vapor deposition (CVD) process using a hot filament with a Hydrogen carrier gas and a hydrocarbon as the Carbon source with an n-type dopant source at 850° C. and 10 Torr pressure.
Ota et al, U.S. Pat. No. 5,201,986, disclose anodic deposition of Diamond from a Hydrogen/hydrocarbon gas mixture using a DC discharge at 1-10 Torr. They also produce Diamond from Hydrogen/hydrocarbon gas mixtures using laser CVD (U.S. Pat. No. 5,387,443).
Kurihara et al, U.S. Pat. No. 5,217,700, produce a good quality Diamond film using a torch technique wherein Oxygen and a hydrocarbon or a Hydrogen/hydrocarbon mixture deposit Diamond film from a flame.
Bailey et al., U.S. Pat. No. 5,470,661, produce Diamond film using plasma enhanced CVD (PECVD) with a Hydrogen free Helium/Acetylene gas mixture.
Gruen et al, U.S. Pat. No. 5,849,079, employ Argon, Hydrogen, and a carbonaceous vapor material (Methane, Acetylene, Fullerene dust) in a high energy discharge that affords a plasma from which a high quality Diamond film is deposited.
Ishikura et al. U.S. Pat. No. 6,060,118, produce Diamond by a CVD method using Methane in Hydrogen and a microwave discharge with a substrate temperature of about 650° C.
Linares et al. U.S. Pat. No. 6,858,080, produce Diamond structures from Methane, Hydrogen and trace Diborane at about 40 Torr using a microwave discharge to produce a plasma.
Chaffin, U.S. Pat. No. 7,306,778, produces Graphite free Diamond films using an inert gas and a Hydrocarbon such as Acetylene with a DC biased radio frequency (RF) discharge.
The methods of the related art form Diamond essentially by decomposition of a carbonaceous source material, and the Carbon so obtained forms Diamond. The present invention forms Diamond by a combinatorial synthesis wherein a first chemical species reacts with a second chemical species to yield Diamond. The conditions of this synthesis are suitable for producing Diamond for microelectronics applications.